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Biomedical Imaging and Instrumentation

Biomedical Imaging and Instrumentation - Poster Session A

Poster G6 - Cleanroom-free Fabrication of Double-Nanohole Plasmonic Tweezers for Label Free Single Molecule Biosensing

Thursday, October 24, 2024
10:00 AM – 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Plasmonic tweezers are a type of optical tweezer that use nanostructured metallic films, in lieu of high-numerical aperture lenses, to physically trap dielectric particles like proteins and nucleic acids with spatial resolution well below the diffraction limit. As a biosensing platform, the intensity of reflected, refracted or diffracted light from these plasmonic tweezers can be used to identify the sizes and orientations of trapped species, as well as individual molecular binding events. However, many current fabrication methods require access to a cleanroom or nanofabrication services, significantly increasing costs. Building on recent research into alternative colloidal lithographic manufacturing techniques, here we developed a cleanroom-free process to make size-tunable, double-nanohole type plasmonic tweezers with standard biochemical lab equipment. The final device design is integrated into a low-cost microfluidic flow-cell to enable the investigation of continuous flow reactions.

Materials and

Methods:  A uniform colloid of spherical SiO2 nanoparticles (SiNPs) was synthesized by the Stöber process at standard temperature and pressure. These nanoparticles were then coalesced into nanodumbbells with the addition of acetone as wetting agent, and permanently encapsulated by a secondary SiO2 synthesis step. Glass microscope slides were silanized in an APTES bath to provide a less expensive adhesion layer for gold than sputtered chrome or titanium. The nanodumbbells were drop-coated onto cleaned glass slides with bovine serum albumin to prevent unwanted aggregation and then sputter-coated in gold. Nanodumbbells were removed by tape exfoliation, leaving dumbbell-shaped nanoholes behind in the gold film. Photosensitive dry film resist was used to create microfluidic channels in relief on top of the patterned gold film. Photomasks with 150 µm resolution were created with a laser-jet printer, and the film resist cured with a 40 W ultraviolet lamp. Uncured features were washed away in a sodium bicarbonate solution with light agitation.

Results, Conclusions, and Discussions: Synthesized SiNPs were measured to have a polydispersity of less than 1% by dynamic light scattering, and the intended morphology of nanodumbbells was confirmed by scanning electron microscopy (SEM). The efficacy of APTES as a gold-adhesion layer was demonstrated until 5% v/v solution at which point no further benefit was observed. The surfaces of drop-coated slides before and after tape exfoliation were compared under SEM to also confirm the transfer of double-nanohole structures. That this platform does not require the labeling or surface adhesion of target molecules, and that experimental data can be collected at the single molecule rather than population level, presents an attractive alternative to existing techniques like surface plasmon resonance and isothermal calorimetry. Future work will include the functional characterization of the described plasmonic tweezers’ trapping efficiency, and lower size limit for binding detection.

Acknowledgements (Optional):